Type 1 diabetes (T1D) is an autoimmune disease characterized by T cell-mediated destruction of the pancreatic islet &#946;cells. NOD mice constitute an extensively studied model for T1D sharing many characteristics with the human disease. Our knowledge of at least some of the &#946;cell antigens targeted by T cells in both NOD mice and T1D patients can now be used practically to develop antigen-based strategies to interfere with pathogenic autoreactive T cell populations and to better understand and augment natural tolerance induction pathways. Dendritic cells (DCs) are critical for the initiation of adaptive immune responses to pathogens. However, in the steady-state, DCs present antigens to T cells in a tolerogenic manner and are important for the establishment of peripheral tolerance. While this was known to be the case in mice that are not prone to the development of autoimmunity, we recently evaluated this concept in the setting of a spontaneous autoimmune disease. We delivered a mimotope peptide, recognized by the diabetogenic NODderived CD8+ T cell clone AI4, to DCs in NOD mice using a peptide-linked antibody to the DC endocytic receptor DEC-205. Proliferation of transferred antigen-specific T cells was initially observed, but this was followed by deletion. Thus, selective antigen targeting of DCs leads to deletion of transferred autoreactive CD8+ T cells even in the context of ongoing autoimmunity in NOD mice with known tolerance defects. While promising, a substantial quantity of additional investigation must be performed before the application of such technology to patients with T1D. Our objectives are to move this strategy in a stepwise fashion to humanized mouse models of increasing relevance to patients with T1D. Four Specific Aims are proposed: Aim 1a. To determine whether targeting of CD8+ T cell epitopes of &#946;cell antigens to steadystate DCs via DEC-205 can result in deletion of endogenous antigen-specific T cells in HLA-A*0201- transgenic NOD mice. Aim 1b. To test the efficacy of antigen targeting to DCs for the prevention of T1D in HLAA* 0201-transgenic NOD mice. Aim 2a. To target preproinsulin to DCs via DEC-205 and monitor the response of endogenous CD8+ and CD4+ insulin-specific T cells in HLA-A*0201-transgenic NOD mice. Aim 2b. To test the efficacy of preproinsulin targeting to DCs for the prevention of T1D in HLAA* 0201-transgenic NOD mice. Aim 3. To determine whether human islet-reactive T cells can be tolerized in response to DEC- 205-mediated delivery of &#946;cell antigens to DCs. Aim 4. To determine the mechanisms responsible for the T cell tolerance observed in response to DEC-205-mediated delivery of &#946;cell antigens to dendritic cells.